In bending presses in particular, relatively long press beams with relatively long working strokes are often employed. In order to guide the elongated press beam in straight movement, it is secured in a known manner to the piston of each of two cylinders that are vertically arranged on the machine frame in spaced parallel relationship to one another. A geometrically similar arrangement is also often found in two-cylinder forming presses. With both types of machines, forming work is performed by a bending or a forming tool which is secured to the beam and which cooperates with a die on the machine table. When asymmetrical workpieces or press tools are employed, there may be exerted upon the beam an asymmetrical force which has a resultant that does not lie midway between the two cylinders on the machine frame, so that different opposing forces are imposed upon the pistons of the two cylinders.
An objective of the present invention is to cause the beam of a press or bending press having an arrangement of the type just described to be constantly guided in motion accurately parallel to the press table, even under the influence of asymmetrical forces.
With a bending press, the bending of the workpiece is obtained by causing the bending tool to ride into the free opening of a die arranged on the machine table. The bending angle of the workpiece is increased as the bending tool rides farther into the opening in the die. From this it can be seen that to obtain a given bending angle for the workpiece, it is essential to effect an arcuate stopping or arresting of the bending tool within the die opening.
An objective of the present invention, therefore, is to achieve in a hydraulic press or the like that has the above described arrangement both an exceptionally accurate parallel guidance of the beam and an exact stopping of the beam upon completion of the working stroke.
The objectives of the invention are thus directed to the solution of a three-fold problem having the following components:
(a) Maintaining parallelism of the beam in relation to the machine table during the feed advance which precedes the working part of the forward stroke;
(b) Exactly stopping the beam relative to the die on the machine table, at a particular desired position;
(c) Maintaining parallelism of the beam in relation to the machine table through the working portion of the forward stroke.